Through magnetic particle testing

ultrasonic testing

metallographic examine

photo-spectrum analysis

and hardness testing etc.for butt weld-joints between the large diameter thick-walled three-way valve on the inlet header of final-stage superheater and the connecting pipe of boiler for a 600 MW unit in one power plant

and combining with crack orientation and crack distritution along the circumferential direnction of weld-joint

it is believed that the main cause leading to cracking in the weld-joints is improper manipulation process in welding and heat treatment.For this

it is recommented to examine 100% weld-joints is this location

and to strictly execute preventive measures specified in the process-guiding instruction.